1. Field of the Invention
The present invention relates to a high-precision liquid projection method and its implementation by a high-resolution printing device in a stimulated continuous ink-jet printer.
A liquid-projection method such as this can therefore be applied to the field of high-resolution printing, but can also be applied to the field of the microdosing of substances used, for example, for the tracing of printed microcircuits or for the application of microdroplets of conductive bonder to fix electronic components on a support or to assemble particles of material according to a given geometry. Another promising application relates to the microdosing of chemical or biological agents in the manufacture of medicines.
2. Description of the Prior Art
In the field of high-resolution printers, a known method, described in the U.S. Pat. No. 4 068 241, is based on the appearance of small drops, called satellite drops, coming from a short filament or column of ink appearing at the upstream or downstream end of a main drop as a function of the value of the amplitude of the vibrational excitation leading to the break-up or separation of the ink jet. Before deflection, the ink jet is constituted by an alternating sequence of main drops and satellite drops, the ratio of the diameters being approximately equal to three. The satellite drops are then deflected according to a "binary" type of deflection technique: to each nozzle of the system, there corresponds only one dot of the pattern to be printed. As a consequence, numerous relative movements between the printing head and the medium to be printed are needed to cover a given surface, and this is a drawback.
As for the main drops, having no charge or low charge, they are recovered and recycled by means of a gutter towards the ink circuit.
Moreover, this printing method-has-another drawback due to its high sensitivity to the process of vibrational excitation of the ink jet. It is difficult to master the reproducibility of the characteristics of the vibrational excitation device without individual adjustment to the mechanical response of each device.
The patent application No. EP 0365454 filed by the Applicant describes a high-resolution printing method implemented in a vibrationally excited continuous ink-jet printer by means of satellite drops.
A continuous ink jet is fractionated into substantially equidistant and equidimensional drops G.sub.n, During the passage of a main drop G.sub.n through charging electrodes, the application of an appropriate electrical voltage V.sub.n makes it possible, in certain specific conditions of use of the jet, to detach the upstream filament of this main drop G.sub.n and hence to create a satellite drop S.sub.n. During the time of formation of the following main drop G.sub.n+1, a voltage V.sub.n+1 with an amplitude substantially equal to V.sub.n is applied so that the satellite drop S.sub.n remains in the jet between the drops G.sub.n and G.sub.n+1 for a period of time that is long enough for it to cross the deflection electrical field located downstream and be thus deflected towards the printing medium. The main drops that have undergone little deflection are recycled in the ink circuit.
The implementation of this method has several drawbacks. First of all, there is the specific character of the conditions required for the desired use of the ink jet. Secondly, the frequency of use of the satellite drops is equal to only a third of that used for the vibrational excitation of the jet: indeed, the drop G.sub.n+1, the electrical charge of which is substantially equal to that of the drop G.sub.n, itself also generates a satellite drop not used for the printing since the value of its charge generally does not correspond to a dot of the pattern to be printed. Furthermore, the electrostatic confinement proposed places the satellite drop in a situation of unstable equilibrium that harms the precision of the deflection. This problem is furthermore aggravated by the length of the path travelled by these satellite drops which pass between the charging electrodes and then into the electrical deflection field.
The goal of the present invention is to overcome these drawbacks by providing a method for the projection of liquid by continuous jets, generating microdrops otherwise than by acting on the amplitude or the frequency of the excitation leading to the breaking up of the jet and not using any additional deflection means apart from that created by the interaction between the drops in the jet.